Since I just finished this game and noticed some discrepancies and missing information, I thought I'd add some notes.
1) Firstly, the second sequence with Thimbletack is in chapter 4, not chapter 3 as some state. I also folllowed this HD video guide and it showed the 29 & 21 cockroaches, and also points out the postage stamp for Thimbletack's house. It is underneath cockroach 39, the video will specifically come back and get it between 48 & 49.
2) They are quests in the Field Guide, but the achievement guides don't mention these. I don't know if they're required for the final story quest to open up, but I found these anyway:
Feather: Deep Woods, near the Oak Treefolk tree it dropped when I killed a Bull Goblin running around here.
Eggshell: Forest Road, after crossing the log near the start and shooting your squirt gun to pass the fire salamanders, it is in the one dead end short path that doesn't lead to one of the many Deep Woods entrances.
Basket: Deep Woods, I believe this is near the entrance you must crawl through from Forest Road near Cypress Treefolk tree and where you'll find 2 of the Garden Sprites.
Elfshot: On the other side of the Cypress Treefolk tree swamp there is an upper path taking you to the Oak Treefolk tree area, it was right by the bit where you drop down into the swamp.
Ring: In the cave after the first Tunnel Troll chase, it is right next to where the second Knocker comes out.
Metal Leaf: Quarry, this is next to the fireplace/cauldron in the Goblin Camp.
Metal Cricket: This is Thimbletack's house item #12, in the caves where you have to lower a stalactite bridge with a gobstone.
3) The achievement guide for sprites regularly talks about Will O' The Wisp Sprite 6, which is one you get from the smashable lanterns in the trees. It is actually referencing Will O' The Wisp Sprite 7, in the initial cave area with a circular path.
4) The final 4 Garden Sprites appear in a specific order that matches the questline in the Field Guide. So specifically you will find Royal Orchid #4, Flowerhead #7 (in the exact same spot, you presumably have to leave then reenter the Deep Woods by the nearby entrance), Flower-Wing #7 and Leatherwing #9. You MUST use the sprite by selecting them with RB and pressing Y to release them, then you should talk with them in the garden (where they will give you a faerie fruit).
5) I had smashed all the lanterns on the tree in the Quarry when I first arrived, but when I was ready for the final Garden Sprite, Leatherwing #9, there was one more lantern to smash that he was inside.
6) Carrying on from that, each of the 4 Garden Sprites will give you another Faerie Fruit. From careful collecting and never using them I had gotten 37, these 4 put me to 41 and the sprite race got me to 46.
7) The best way to win the race is to have 2 Flower-Wing dash sprites and any 3rd sprite to fill up your inventory. Otherwise I found the game loves to followthrough with your A button press to end the conversation and swing your net if it's equipped, thus catching the sprite instantly. 2 dash sprites is more than enough to dash through the entire race and win easily. If you accidentally catch the racing sprite, use it then just go back in the house to cancel the race. He will give you 5 Faerie Fruit, and probably 5 each for Gobstones and Ball Bearings if you are having problems getting those achievements - also don't forget the 15 ball bearings in the washing machine in the cellar and the 60? gobstones from the second Knocker.
8) Bellflower #5 was my final sticking point, it was never at the Cypress Treefolk tree as stated in the guide. Buckyfellini
pointed out that you must crawl through the log, and then it will fly around this log.